Antenna



Jul'y 9, 1935.

P. s. CARTER ANTENNA Filed Jan. l5, 1954 )00M l 29; U

/f/GH Ffaaf/Vfr 4P/2464705 `INVENTOR P. .5. CArE/ BY A TTORNE Y Patented July 9, 1935 ZMQLGM) arent ,ric

ANTENNA Philip S. Carter, Port lleierson, N. Y., assigner to Radio Corporation of America, a corporation of Delaware Application `lanuary 13, 1934, Serial No. 706,530

2 Claims..

This invention relates to improvements in antenn, and one of its objects is to obtain from a radiating system an increase in concentration of radiation in the direction perpendicular to the antennand, simultaneously therewith, an increase in radiation eiiiciency. A lvfurther object is to provide a system whose natural wave length of oscillation is less than that oi the ordinary type of antenna customarily employed for communication purposes.

Both of these objects are accomplished, in accordance with the invention, by providing a radiating antenna with a variable cross-section constructed in such manner that the diameter varies approximately logarithmically.

1t has been the practice in the past,V in communication by radio, to employ as radiating elements one or more wires oi' constant diameter. When these are used for broadcasting purposes, it has been usual to suspend these radiating wires between two talltowers. By means oi the present invention, however, and according to one embodiment thereof, the tower itself is used -as a radiator and its eiiectiveudiameter made to vary in a. substantially logarithmic manner so as to obtain an increase in radiation resistance, as a consequence oi which there is obtained an increase in the radiation eiiiciency and adecrease in high angle radiation, a result which reduces fading at the receiver due to causes such as interference between the waves radiated at high angles and ground waves. In the short wave field, however, where there are used wires of constant diameter having lengths approximately equal to half the length of the communication wave, the principal advantage oi the invention lies in the increase in directivity obtained, as compared with the ordinary half Wave length dipole radiator.

One important advantage oi the present invention resides in the existence of a continual change in the characteristic impedance of the radiating line which results in a desirable current distribution therein. To illustrate, if the ordinary antenna oi constant diameter having a length equal to half that of the commimication wave werer lengthened, the current therein would reverse, whereas by utilizing an antenna of variable cross-sectio-n in accordance with the invention, the current distribution is made to be very much like that in a half wave length line.

Referring to the drawing, Figure 1 illustrates, schematically, lan antenna of the dipole type built according to the principles underlying the (Cl. Z50-33) present invention, and Figure 2 illustrates one of the embodiments which the structure of Figure l might take; Figure 3 illustrates an antenna where the tower itself comprises the radiating element, and Figure 4 shows an antenna utilizing only one haii of the system oi Figure 2.

A general outline of the theory of the operation of the invention follows: It is well known that the coeicients of inductance and capacity for a radiator having a constant diameter are very nearly equally distributed along its line, and that such a distribution of these constants can be shown mathematically to result in a sine wave distribution of the current. When the diameter of a radiator is made to Vary logarithmically, the coei'cient of inductance varies in a linear manner with the distance, but the coefficient of capacity varies in an inverse manner to that of inductance, so that the square root of the product of the two always remains equal to the reciprocal of the velocity of light. The resulting differential equation for the variation of the current along the wire is of the Bessel type. The general form of the current distribution is given by the sum of two aero order Bessel functions of the iirst and second kind, each multiplied by constants determined by the particular conditions. The argument in these functions is a factor depending upon the ratio ci the maximum to minimum value oi inductance and the distance from the ends. For the resonance condition the natural wave length Will lie within the limits of 1.25L and 2L, where L is the length, depending upon the particular logarithmic law of Variation in the diameter. In the ordinary radiator the natural wave length, disregarding end eiects, is 2L. The current distribution for the radiator described in this invention, although theoretically givenv in terms of Bessel functions is of approximately a sine wave form wherein the velocity of propagation is assumed to be greater than light by the ratio oi 2L to its natural wave length. Such a velocity is, of course, impossible but in the steady state the current distribution is approximately the same as though it actually existed.

By integration of or summing up the energy flow over an imaginary sphere surrounding this radiator, we find a considerable increase in radiation resistance as compared to that for the ordimay be cut at the center and one half used above ground, the second half being considered as the image below ground of the actual radiator used. Such an arrangement is illustrated in Figure 4. A further embodiment is illustrated in Figure 3 which discloses the usual type of tower so shaped as to have a substantially logarithmic variation in diameter, the lattice work forming, in effect, a cage of wires without straying from the limitations of good structural engineering practice.

It is to be understood, of course, that the invention is not limited to the modifications shown, since there are any number of modications varying considerably in structural details which will fall Within the spirit and scope of the invention.

I claim:

1. An antenna comprising a horizontal dipole, said dipole having an over-all diameter which is greatest at its center and which decreases from the center toward both ends, and a. two wire transmission line connected to said dipole at points symmetrically disposed with respect to the center of said dipole.

2. An antenna comprising a horizontal dipole composed of an interconnected plurality of conductors, said dipole having an over-all diameter which is greatest at the center and which decreases from the center toward both ends, and a two wire transmission line connected to said dipole at points symmetrically disposed with the center of said dipole.

PHILIP S. CARTER. 

